This invention relates generally to diagnostic radiography, and, more specifically, to x-ray anti-scatter grids for improving x-ray image contrast.
During medical diagnostic radiography processes, x-rays are directed toward an object from an x-ray source. When x-rays are used to create an image of an object, a portion of the radiation, i.e., direct radiation, passes directly through the object unimpeded from the x-ray source and onto an x-ray detector to create an x-ray image on a photosensitive film or other suitable detector. Some of the direct radiation is differentially absorbed by the object, which creates a shadow of the object on the film or detector. A portion of the radiation is scattered and arrives at the x-ray detector at an angle which deviates significantly from its original path from the x-ray source. The scattered radiation results in a xe2x80x9cveilxe2x80x9d superimposed on the absorption image, thereby reducing contrast of the radiograph image. To counteract the reduced contrast due to scattered radiation, the amount of radiation exposure to the object is often increased. If scattered radiation is reduced or eliminated, contrast of the image can be enhanced, the radiation dose to the object (or patient) can be reduced, or both.
Radiation scattering can be reduced by using an x-ray anti-scatter grid. Anti-scatter grids are typically fabricated from thin sheets of x-ray absorbing material arranged in a geometric pattern to absorb scattered radiation, and a non-absorbent, fiber-like spacer material between absorbent sheets that allows direct radiation to pass through the anti-scatter grid. In one type of anti-scatter grid, known as a focused grid, the absorbent sheets are arranged approximately parallel to the direct x-ray beams emanating from an x-ray source. In a further type of anti-scatter grid, known as a focused cross grid, the absorbent sheets are arranged in a mesh and focused along two substantially perpendicular axes. The cross grid is focused in two dimensions, and requires precise positioning of the anti-scatter grid relative to the x-ray source. The focal lengths of the focused grids are typically fixed, and the relative location of the x-ray source and anti-scatter grid must remain fixed to achieve acceptable radiograph results. It would be desirable to provide a variable focal length grid to allow more flexibility in setting up x-ray procedures.
Focused anti-scatter grids are typically manufactured by laying-up, or stacking, alternate layers of absorbing material and spacer material and bonding them together. The grid components are aligned during assembly to obtain the desired focus. Alternatively, very fine slits are formed in an x-ray transparent material in a focused pattern, and the slits are filled with x-ray absorbing material to form a focused grid. See, for example, U.S. Pat. Nos. 5,557,650 and 5,581,592. In yet another manufacturing technique, a photo-resist and chemical etching process is used to fabricate slightly different layers of absorbing material in a mesh like pattern. The layers are stacked and appropriately bonded to form a focused cross grid. See, for example, U.S. Pat. Nos. 5,606,589 and 5,814,235. Each of the above manufacturing methods, however, are complicated and tedious, and often result in large variations in grid quality.
Accordingly, it would be desirable to provide a focused anti-scatter grid that may be manufactured more quickly and easily in comparison to known x-ray grids. In addition, it would be desirable to provided an anti-scatter grid that has an adjustable, or variable, focal length.
In an exemplary embodiment of the invention, an x-ray anti-scatter grid includes an integrally formed geometric grid structure defining a plurality of spaces. An inter-space material is located in the spaces, and the grid structure and inter-space material are configured to flex along at least one axis, thereby changing an effective focal length of the grid.
More specifically, the grid structure is injection molded and fabricated from a thermoplastic material to form a rigid but flexible grid that may be flexed along at least one axis to change the effective focal length of the grid. An injection molded cross grid could be flexed along a second axis to further improve x-ray image contrast. By injection molding the grid from thermoplastic material, labor intensive manufacturing techniques of known anti-scatter grids may be avoided, and hundreds of anti-scatter grids may be manufactured quickly and inexpensively.
Also, injection molding allows air to be used as the inter-space material, rather than fiber-like, low density material used in conventional anti-scatter grids. Because the fiber-like material absorbs a measurable portion of x-rays, by eliminating the fiber-like material, radiation energy that reaches the x-ray detector is increased. Consequently, a higher quality image is realized with a given radiation dose, or conversely, the radiation dose can be reduced while still achieving a high contrast image comparable to known anti-scatter grids.
Therefore, a more versatile anti-scatter grid is provided that may be manufactured more quickly and easily relative to known anti-scatter grids, thereby reducing manufacturing costs of anti-scatter grids.